The invention relates to a process for the detoxification of the exhaust gases of an internal combustion engine including a fuel metering system which is controlled by an oxygen measuring sensor disposed on the exhaust side of the engine.
As is well known, the concentration of toxic hydrocarbon compounds and carbon monoxide is especially low in a slightly leaned-out air-fuel mixture. On the other hand, it is especially in this mixture domain that toxic nitrogen oxide components are present in large quantity. In richer air-fuel mixture domains, the nitrogen oxide components are present in lesser quantity. Thus, it has been proposed to operate a fuel metering system at a setting which provides a slightly enriched mixture, (.lambda.&gt;1) so that the exhaust gas will contain relatively few NO.sub.x components and to oxidize any remaining excess of carbon monoxide and hydrocarbon compounds by admitting a secondary stream of air to the exhaust gas. The parameter .lambda. is called the "air number" and is defined as being proportional to the ratio of the mass of air to the mass of fuel. When the air-fuel mixture is a stoichiometric mixture, .lambda. = 1.0. Aside from the fact that such a process necessitates high fuel consumption, difficulties arise during the warm-up operation of the internal combustion engine and also when very low outside temperatures prevail, because under those conditions, regulartory deviations may occur due to the wide control region involved and the dead-time of the control process also becomes too large.